1. Field of the Invention
The present invention relates to an adhesive system which is suitable for use in adhering an incompatible ink system to a polymeric film. More particularly, the present invention relates to a polymeric sheet having an incompatible ink permanently bonded thereto, and specifically a floor covering having a lithographic ink or electrographic toner bonded to a primer which is bonded to the floor covering.
2. Related Art
The term incompatible refers to the inability of the ink system to directly and permanently bond to a polymeric sheet only through solvent or carrier evaporation. An example of a compatible system would be the case in a typical rotogravure vinyl ink system when it is printed onto a rigid polyvinyl chloride (PVC) film.
To create a high quality colored (nearly photographic, i.e., better that 150 line rotogravure) decorative design on surfaces of tile products, the rotogravure printing technique is the state of the art technique most often selected. While this printing technique is relatively easy to operate, it has some drawbacks. It is capital intensive, in that new designs require new printing cylinders prior to printing. It requires long lead times to prepare the cylinders for printing. In addition, this technique is geared to high volume printing and usually on relatively thin webs, i.e., 1.5 to 10 mils in thickness. Clean up of the printing cylinders is more time consuming than most of the actual print run, resulting in potentially high labor costs associated with the actual job, and a natural tendency to make the runs longer than are necessary.
In order to provide a lower cost, short run, and faster turnaround printing system, a departure was made from the current rotogravure printing system. Two high quality four color printing techniques, lithographic and electrographic printing, offered these opportunities. However, it became obvious that the conventional ink systems used in these techniques were not compatible with the polymeric films that are used in the manufacture of polymeric sheet products.
In the lithographic process, which can be a sheet-fed printing process, the inks cure by oxidation. After printing on rigid PVC film, the ink will still be soft after drying. The image will readily smudge and result in an unacceptable print. This actually occurs to some extent in normal conventional lithographic printing of paper today if one were to examine a four color process-printed page in a magazine or on an advertising poster. It has been found that when a conventional-lithographic printed PVC film is bonded conventionally to a floor tile base, the ink layer will not impart the proper adhesion requirements after lamination for an adequately performing product.
The same is true of the electrographic printing systems where the colored images are formed on the film using both liquid and dry toners. Even, when the electrographic printing (e.g., from a Savin color copying machine) is done on specially treated papers and films, the ink layer which is actually to act as the adhesive layer between the clear protective film and base or substrate after lamination is not strong enough to prevent delamination in use.
Scopp U.S. Pat. No. 3,725,184 discloses a coated vinyl film. The laminated article contains a polyvinyl chloride, polyvinyl acetate and polyvinyl alcohol layer interposed between an exposed vinyl layer and the printing on the surface of a vinyl core to improve the adhesion between the exposed layer and the printing ink. Scopp specifically teaches using an ink which is compatible with the vinyl core, whether the core is a calendered vinyl sheet or an extruded vinyl sheet. The compatible ink is applied most frequently by off-set lithography or dry off-set printing methods.
Wheeler U.S. Pat. No. 3,330.684 relates to printing ink compositions suited for printing on polymeric materials by lithographic and letterpress printing processes. The Wheeler inks include as essential constituents, dispersed spherulites of high density polyethylene, a colorant and a binder for the polyethylene and the colorant. The spherulites are dendritic spherulites of high density polyethylene having a density of at least 0.95.
Haggas et al. U.S. Pat. No. 3,667,983 discloses the use of conventional lithographic and letterpress inks which are printed on flexible thermoplastic sheets. Adhesion is improved by overcoating the printed ink with a synthetic lacquer which permeates the printwork and serves both as a bonding agent and as a protective coating. Haggas et al. state that the basic material of the synthetic lacquer must be selected to match the sheet material to be color printed. They recommend butyl methacrylate/methyl methacrylate copolymer based lacquer for polyvinyl chloride.